Question
Describe the structure of the adrenal gland. What are the functions of adrenaline and cortisol? How do these two hormones differ in their action?
Solution — Step by Step
The adrenal glands (also called suprarenal glands) are two small, triangular glands sitting on top of each kidney. Each gland has two distinct regions:
- Adrenal cortex (outer region): Makes up ~80-90% of the gland. Secretes steroid hormones.
- Adrenal medulla (inner region): Makes up ~10-20%. Secretes catecholamines (adrenaline and noradrenaline).
These two regions are functionally distinct — they have different embryological origins and secrete completely different types of hormones.
Secreted by: Adrenal medulla.
Stimulus for secretion: Stress, fear, danger, excitement — the “fight-or-flight” response. The hypothalamus triggers sympathetic nervous stimulation of the adrenal medulla.
Actions:
- Increases heart rate and cardiac output
- Dilates bronchioles (airways) — improves breathing
- Increases blood glucose (by stimulating glycogen breakdown — glycogenolysis)
- Dilates pupils
- Redirects blood from digestive organs to muscles
- Increases mental alertness
Together, these effects prepare the body to fight a threat or run from it — hence “fight-or-flight.”
Secreted by: Zona fasciculata of the adrenal cortex.
Stimulus for secretion: Prolonged stress, low blood glucose, ACTH (adrenocorticotropic hormone) from the anterior pituitary.
Actions:
- Glucocorticoid effects: Raises blood glucose by promoting gluconeogenesis (glucose synthesis from proteins and fats) and inhibiting glucose uptake by cells
- Anti-inflammatory: Suppresses immune response and inflammation
- Protein catabolism: Breaks down proteins to provide amino acids for gluconeogenesis
- Fat mobilisation: Breaks down fat stores
Cortisol is the hormone of sustained stress — it keeps blood glucose elevated when the body needs prolonged energy.
| Feature | Adrenaline | Cortisol |
|---|---|---|
| Source | Adrenal medulla | Adrenal cortex |
| Chemical nature | Amino acid derivative (catecholamine) | Steroid |
| Onset | Rapid (seconds) | Slow (minutes to hours) |
| Duration | Short-lived | Long-lasting |
| Trigger | Acute stress | Chronic stress, low blood glucose |
| Main effect | Fight-or-flight response | Gluconeogenesis + anti-inflammation |
Why This Works
The adrenal gland’s dual structure makes evolutionary sense. When you face sudden danger, you need immediate response — adrenaline from the medulla acts within seconds. When you’re under prolonged stress (fasting, illness, chronic anxiety), you need sustained energy management — cortisol from the cortex provides this over hours.
The receptor mechanisms differ too: adrenaline binds to surface receptors (adrenergic receptors) and acts through second messengers (fast). Cortisol, being a steroid, crosses the cell membrane and binds to nuclear receptors, directly regulating gene expression (slow but prolonged).
Alternative Method — Remember by “AM and AC”
AM (Adrenal Medulla): A for Adrenaline — Acute/rapid response. AC (Adrenal Cortex): C for Cortisol — Chronic/sustained response.
Common Mistake
Students often confuse the cortex and medulla. Remember: cortex is outer (like the bark of a tree — cortex = bark in Latin), medulla is inner (like the core/marrow). Adrenaline comes from the inner medulla; cortisol comes from the outer cortex. A simple way to remember: “A is for Adrenaline, A is for inner (core) of Apple.”
NEET frequently asks about the hormone and its source together. Never write “adrenal gland secretes adrenaline and cortisol” without specifying medulla vs cortex — you lose a mark. Always write “adrenal medulla secretes adrenaline” and “adrenal cortex secretes cortisol.”